1. Field of the Invention
The present invention relates to a catalyst for oxidizing carbon-containing compounds and a method for the production of the same. More particularly, the present invention relates to a catalyst whose performance is not deteriorated at catalyst temperatures of 800.degree. C. or higher and which is useful for catalytic oxidation of gaseous fuels or exhaust gases containing one or more combustible gases such as hydrogen, carbon monoxide, methane, propane, and butane, liquid fuels such as kerosene, gas oil, and alcohols as well as combustible organic compounds, and a method for the production of the same.
2. Description of the Prior Art
It is a recent trend that the use of catalytic oxidation has been increasing in order to oxidize gases containing a high concentration of a fuel or a combustible component (such as an organic solvent or a hydrocarbon) to produce gas at high temperature is then used directly as a heat source for a heater, boiler, gas turbine or the like, or indirectly as a heat source for a boiler by means of a heat exchanger.
Among these sources, systems exist whose catalyst temperature was reach 700.degree. C. or even be as high as 1,400.degree. C. Hence, at such high temperature regions, not only heat resistance sufficient for retaining the performance of the catalyst becomes necessary, but also the use of an oxidation catalyst having a high activity in order to cope with a high space velocity, SV, (gas flow per unit time/volume of catalyst) or a high linear velocity, LV.
As the aforementioned type of catalyst, those catalysts comprised of a carrier composed of .gamma.-alumina, silica, or silica-alumina, having thereon platinum and/or palladium are known to be most active and used widely.
However, the conventional catalysts suffer from a loss of carrier surface area such as .gamma.-alumina, silica, or silica-alumina when they are exposed to high temperatures. When platinum catalysts are used at temperatures above 600.degree. C., fine platinum particles dispersed in the catalysts aggregate, resulting in a decrease in the catalytic activity. It is generally known that, for palladium catalysts (which have an excellent resistance to heat during vapor phase oxidation reactions), palladium oxide, i.e., active species, is converted to reduced palladium at a temperature near 830.degree. C. so that the oxidation activity of the catalyst decreases abruptly. Hence, in the case of catalytic oxidation of high concentration gases, various special measures have been considered. That is, trouble has been taken to dilute the gases with the air to decrease the concentration of combustible components so that the catalyst temperature during the oxidation reaction will not increase to 600.degree. C. or higher, or use is made of a plurality of catalyst layers of which an upstream catalyst layer is made of a catalyst having a coarse-mesh honeycomb support carrying palladium and/or platinum thereon to physically decrease the reactivity of the catalyst while controlling outlet gas temperature to 600.degree. to 800.degree. C. or less so that the catalyst can be free of undue thermal load. The former is disadvantageous in that it calls for an apparatus of a larger size and a larger amount of catalyst, which is uneconomical. On the other hand, the latter generally gives only insufficient results because a portion of combustible components remain unused.
Japanese Patent Application Laid-Open No. 113487/1975 proposes calcination of a mixture of metal oxides such as calcium, strontium, barium, silicon, tin and the like as a means for improving the thermal resistance of a carrier such as .gamma.-alumina. However, the composite oxides are still insufficient in their thermal resistance.